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Dawn at Vesta III

The Dawn spacecraft captured this image of the asteroid Vesta from a distance of just 26,000 miles (41,000 km) on July 9. Dawn entered orbit around Vesta on the night of July 15, at an altitude of less than 10,000 miles. It will spend about one year studying the large, rocky body before proceeding to a second destination: Ceres, the largest asteroid. [NASA/JPL/UCLA/MPS/DLR/IDA]

Vesta is an asteroid with a difference. Unlike almost all the other rocky bodies in the asteroid belt, Vesta is probably layered, as Earth and the Moon are.

We should know a lot more about those layers soon, because the Dawn spacecraft is scheduled to enter orbit around Vesta tomorrow. It'll study the asteroid for a year before heading for the largest asteroid, Ceres.

Vesta is the third-largest asteroid, with a diameter of about 335 miles. When it formed, it got hot enough to melt its interior. That allowed lightweight rocks to float to the surface, while heavier ones pooled at the center. So like Earth and the Moon, Vesta has a metallic core, a mantle of lighter rocks around it, and a crust of the lightest rocks on the top.

Christopher Russell, Dawn's principal investigator, explains:

RUSSELL: Vesta is essentially like a small Moon. If you take a look at the reflected light from Vesta, there will be many similarities to the reflected light from the Moon, and the material is very similar.... Vesta, from the meteoritic evidence, the meteorites that have fallen on the Earth, those meteorites tell us that the material that came from Vesta is depleted in iron, as if some of the iron has gone into the core. So we're pretty sure that we've got a complete package here of a very Moon-like body with a small iron core.

When Dawn's work at Vesta is done, we should have a profile of the asteroid that is more than skin deep.

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